It's been some years since I was there, and it was in my Grady White 24, so I wasn't looking for >5' depths like you will be. There will always be some shoaling in dredged channels like those leading to Ewell, so if you go, you'd better go slowly and check your ranges both fore and aft so you stay in the marked channel.
There's a marina in Ewell that has a few slips for transients, but it would be a good idea to call or
email. I believe it's called the Smith Island Marina (surprise!). I don't
recall any place for
anchoring, and the way the watermen roar out around dawn to go to
work, you're better off in a slip. You could also ask the marina people about
current depths in the approach channels.
Here's a
Google Earth image of Ewell. You can see how constrained the "good"
water is there. It's worth a try, if only for the crab cakes!